The project aims at a better understanding of sensory processes. Because of its breadth, timely specific problems are selected for study, and for appropriate periods of time, the main effort is concentrated on them. For the coming year, our research plans call for a continuation of microelectrode recordings from single fibers of mammalian auditory nerves. Our recent research has strongly indicated that the inner and outer hair cells of the cochlea interact in phase opposition. This appears to be true at least for characteristic frequencies below 5 kHz. The inferred interaction brings up problems of stability of amplitude and phase relationships between the two cell populations. We will begin to study these problems with the help of variation of stimulus parameters and toxic effects on the neural and sensory units of the cochlea and the auditory nerve. We will also study the relationships in units with high characteristic frequencies where the interaction should be based on "d.c." rather than "a.c." processes. In addition, we will study responses to incremental stimuli, which in the past three years permitted us to clarify some problems of nonlinearity and short-term temporal adaptation. In particular we could shown that the adaptation results from an additive rather than from an automatic gain-control process. Psychophysical experiments on central auditory masking and experiments on the acoustic middle-ear reflex are also planned. These experiments are conceptually related to our neurophysiological studies.